Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain or discomfort with altered frequency of defecation and stool consistency. Some people with IBS also experience urgency for bowel movements, feeling of incomplete stool evacuation, straining and cramping during defecation, presence of mucus in stool, abdominal distention and flatulence. IBS is believed to be the consequence of several factors: altered bowel motility and sensitivity (visceral hypersensitivity), altered brain-gut axis function, low-grade mucosal inflammation, disturbed balance of intestinal microbiota, chemical irritation, action of psychogenic factors and (at least in some cases) genetic predisposition. When there are no alarm signs, the diagnosis of IBS can be made on the basis of clinical presentation alone. When alarm signs, such as rectal bleeding, fever, high erythrocyte sedimentation rate, weight loss, failure to thrive (children) or positive family history for organic bowel disease (chronic inflammatory bowel disease, cancer) are present, accurate diagnostics is necessary. When treating patients with IBS, education and a trustful patient-doctor relationship are necessary, with emphasis on IBS being a benign disorder that only rarely leads to serious consequences. Some patients benefit from excluding nutrients that are known to cause discomfort from their diet. However, most patients do not need a specific diet. Special probiotics having effects validated by high-quality clinical trials may be useful in treating patients with IBS. When mental factors play an important part, psychotherapy may also have a role. The use of medications, however, is reserved only for resistant forms of IBS.